What's on this page?
- Introduction
- Methods of Home Food Preservation
- Food Preservation Resources page lists resources we use for up-to-date, research-tested methods and recipes.
Introduction
Excerpts from Historical Origins of Food Preservation by Brian A. Nummer, Ph.D., National Center for Home Food Preservation, May 2002. Reprinted with permission of the University of Georgia. B.A. Nummer. 2002. Historical Origins of Food Preservation. Athens, GA: The University of Georgia, National Center for Home Food Processing and Preservation. The astonishing fact about food preservation is that it permeated every culture at nearly every moment in time. To survive ancient man had to harness nature. In frozen climates he froze seal meat on the ice. In tropical climates he dried foods in the sun. |
Commercially Available Preserved Foods
Supermarkets are full of foods that have undergone one or more processes to delay spoilage. Refrigerators and freezers provide cold storage. Aisles of packaged goods are stocked with foods preserved by various methods, often with chemical additives to make them shelf-stable.
Excerpts from FSIS.USDA.gov Shelf-Stable Food Safety
Foods that can be safely stored at room temperature, or "on the shelf," are called "shelf stable." These non-perishable products include jerky, country hams, canned and bottled foods, rice, pasta, flour, sugar, spices, oils, and foods processed in aseptic or retort packages and other products that do not require refrigeration until after opening. Not all canned goods are shelf stable. Some canned food, such as some canned ham and seafood, are not safe at room temperature. These will be labeled "Keep Refrigerated."
In order to be shelf stable, perishable food must be treated by heat and/or dried to destroy foodborne microorganisms that can cause illness or spoil food. Food can be packaged in sterile, airtight containers. All foods eventually spoil if not preserved.
Except for infant formula and some baby food, product dating — having a "use-by," "sell-by," or "best-if-used-by" date —
is not required by Federal regulations. Dating is for quality, not safety. [Click to read more from FSIS.USDA about Food Product Dating.]
Will commercially canned goods last forever? [NO!]
Commercial canning is done under tightly controlled conditions — careful sanitation and the necessary time and temperature under pressure, but there are still limits to how long it will preserve food. There are several factors that limit the shelf life of canned foods. First, cans can rust over time. Shipping accidents, where cans fall and dent or are crushed, also cause container problems.
Then there's can corrosion. In all foods, but especially in high-acid foods like canned tomatoes, natural chemicals in the food continually react with the container. Over several years, this can cause taste and texture changes, and eventually lower the nutritional value of the food.
High temperatures (over 100 °F) are harmful to canned goods too. The risk of spoilage jumps sharply as storage temperatures rise. In fact, canned goods designed for use in the tropics are specially manufactured.
Store canned foods and other shelf stable products in a cool, dry place. Never put them above or beside the stove, under the sink, in a damp garage or basement, or any place exposed to high or low temperature extremes. Temperatures below 85 °F are best. Check your pantry every few weeks and use canned goods you have had on hand for awhile. Don't purchase bulging, rusted, leaking, or deeply dented cans.
Preserving at Home
No matter why we choose to preserve at home, we want the results of our efforts to be of good quality and safe to eat. The USDA and extension programs have published guidelines for safe home food preservation methods and recipes based on research and extensive testing. Watch UC Master Food Preserver Food Safety Training (a series of 11 videos that the University of California has made available to the home consumer) to understand the science behind food quality and safety. Video topics include food spoilage, microorganisms found in food the can be hazardous and environmental factors that affect the rate at which they multiply.
NOTE: Research is ongoing - recommendations may change. Please refer to the National Center for Home Food Preservation (NCHFP) for the most current recommendations.
Start with food of good quality and adhere to food safety guidelines: clean - separate - cook - cool. Remember: If food doesn't look or smell right, it is better to throw it out than to risk your health.
Methods of Home Food Preservation
Historical Origins of Food Preservation describes Drying, Freezing, Fermenting, Pickling, Curing, Jam and Jelly, and Canning. Our web pages cover drying, freezing, and canning of pickled foods and jams and jellies.
Cold Storage (Refrigeration and Freezing)
Reducing the temperature at which food is stored slows the growth of food spoilage microorganisms and enzymatic reactions within food.
Many, but not all foods benefit from cold storage. Know where to Store Fresh Fruits and Vegetables for Better Taste. (See Food Safety page for information about storing leftovers.)
Refrigeration
Refrigeration does not kill microorganisms that can spoil food, but storing food in a refrigerator set below 40 degrees Fahrenheit will slow the rate at which foodborne bacteria multiply. Inside the refrigerator's controlled conditions, food items can stay fresh and usable longer than at the ambient room temperature.
Refrigeration is the most common preservation tool in use.
- Keep refrigerator below 40° F
- Use a thermometer
- Keep foods from contaminating other foods – meats below fresh produce.
- Pay attention to package dating
- When in doubt, throw it out!
Freezing
Modern freezing is one of the easiest, longest lasting techniques we have. It is also the most convenient if care is taken in the freezing process.
Factors Affecting Quality of Frozen Food
- Enzymes - freezing slows enzymes, blanching can improve color and texture of certain foods
- Air - oxygen can cause flavor and color changes in improperly packaged food
- Microorganisms do not grow at freezing temperatures but are not destroyed
- Ice Crystals - the smaller the better, the quicker something freezes the smaller the crystals
- Freezer temperature - 0° or lower (use an in freezer thermometer)
- Evaporation of Moisture - proper packaging helps with evaporation of ice crystals that cause dried out, or freezer burned food
Freezing Pointers
- Freeze foods at 0°F or lower. To facilitate more rapid freezing, set the temperature control at -10°F or lower about 24 hours in advance.
- Freeze foods as soon as they are packed and sealed.
- Do not overload your freezer with unfrozen food. Add only the amount that will freeze within 24 hours, which is usually 2 to 3 pounds of food per cubic foot of storage space. Overloading slows down the freezing rate, and foods that freeze too slowly may lose quality.
- Place packages in contact with refrigerated surfaces in the coldest part of the freezer.
- Leave a little space between packages so air can circulate freely. Then, when the food is frozen, store the packages close together.
- Leave proper headspace to allow for expansion
Packaging for Freezing
- Moisture vapor resistant
- Durable and leak-proof
- Not become brittle and crack at low temperatures
- Resistant to oil, grease or water
- Protect foods from absorption of off flavors or odors
- Easy to seal
- Easy to mark
Other Important Things to Know
- Blanching helps improve the color and texture of frozen food
- IQF - Individual Quick Freezing: spread food on a tray and freeze, then repackage. Works well for fruits and some vegetables
Thawing
- Refrigerator Thawing - plan ahead as this is the safest way for meats
- Cold Water Thawing - faster but requires attention and can waste water
- Microwave Thawing - fine for certain foods, but uneven, can start cooking
- Cooking Without Thawing - move food straight from freezer to pot
Perishable foods should always be thawed in the refrigerator!
More Information
http://usda.gov and search for the topic you are interested in.
Examples of searches are: mold, refrigeration, food safety
Drying (Dehydration)
Drying (dehydrating) food is one of the oldest and easiest methods of food preservation. Dehydration is the process of removing water or moisture from a food product. Removing moisture from foods makes them smaller and lighter. Dehydrated foods are ideal for backpacking, hiking, and camping because they weigh much less than their non-dried counterparts and do not require refrigeration. Drying food is also a way of preserving seasonal foods for later use.
How dehydration preserves foods
Foods can be spoiled by food microorganisms or through enzymatic reactions within the food. Bacteria, yeast, and molds must have a sufficient amount of moisture around them to grow and cause spoilage. Reducing the moisture content of food prevents the growth of these spoilage-causing microorganisms and slows down enzymatic reactions that take place within food. The combination of these events helps to prevent spoilage in dried food.
The basics of food dehydration
Three things are needed to successfully dry food at home:
- Heat — hot enough to force out moisture (140°F), but not hot enough to cook the food;
- Dry air — to absorb the released moisture;
- Air movement — to carry the moisture away.
Foods can be dried using four methods:
- In the sun — requires warm days of 85°F or higher, low humidity, and insect control; recommended for dehydrating fruits only;
- In the oven — drying in an oven uses the most energy. It is possible if you can set your oven temperature very low. Some recommend propping the oven door open to let moisture evaporate. A convection oven often does a good job dehydrating food as it uses the fan function to facilitate drying
- Solar dehydrator: a solar dehydrator is an enclosed structure that uses natural convection to move the warm air over the food inside. Sometimes called an Appalachian Dehydrator. Plans are available from many websites.
- Using a food dehydrator — electric dehydrators take less time to dry foods and are more cost efficient than an oven. Look for one with UL Seal of Approval for safety. Older models are not always safe.
Methods
Choose a fruit or vegetable in great condition. Drying will not make a fruit become better than it is. If you do have fruit that is getting too soft, you can make a purée and make fruit leather.
Cut your produce into thin slices. The thinner the slice the faster it will dehydrate. Too thin, though, could make a final product that is so thin in breaks into pieces.
As you cut up certain fruits, such as apples and pears, you will need to drop them into a bowl of acidified water. You can use lemon juice, ascorbic acid (vitamin C), or citric acid to help prevent unwanted browning of the fruit.
Many vegetables benefit from blanching prior to dehydrating. Fill a large pot with water and bring to a boil. Place prepared vegetable in the water. Bring back to a boil. See the USDA guide for timing guidelines for each vegetable.
http://nchfp.uga.edu/how/dry/csu_dry_vegetables.pdf
Place the produce in a single layer on the trays of the dehydrator. Set the temperature to the correct setting for what you are drying. Most fruits and vegetables are dried at 125° to 135° while herbs are dried at a much lower temperature and meats for jerky are at a higher temperature.
After dehydration, check food to see if it is pliable but not moist. Place food in a container and shake daily for several days to condition, which distributes the moisture evenly, and check for condensation. If there is any moisture, return the food to the dehydrator. If you have used a method for dehydration that could have allowed insect access to the food, it is recommended that you freeze the food to kill any bugs or insect eggs.
Store dehydrated food in an airtight container in a cool, dark place for the best quality. Dried foods maintain the best quality and nutritional value if they are used in less than 12 months. Dried foods may still be edible after many months or years in storage, although they may not be as tasty or nutritious.
Fruit Leathers
Fruit leathers can be made by puréeing fruit and pouring the fruit on a special fruit leather tray. Mixing the purée with applesauce or instant pectin makes for a more flexible final product. Follow the directions on the pectin for the amount of pectin to add.
Visit the USDA website for further information and recipes: http://nchfp.uga.edu/how/dry.html
Learn more
- Drying Fruits and Vegetables (University of Georgia Extension)
University of Georgia Cooperative Extension: resource UGA "Preserving Food: Drying Fruits and Vegetables" - Drying Fruits and Vegetables (Pacific Northwest Extension Publication PNW397)
Pacific Northwest Extension Publication PNW397: Drying Fruits and Vegetables (PNW 397)
Pickling and Fermentation
Lacto-Fermentation - An Overview
Lacto-Fermentation is a metabolic process that converts sugar to acids, gases, and/or alcohol. Lactic acid bacteria breaks down a food and in the process lowers the pH of the food making it more acidic. Examples of this are cucumbers turned into pickles and milk turned into yogurt.
Lactobacillus strains are the main microorganisms in fermentation with a few other microorganisms assisting. Lactobacillus are also referred to as lactic acid bacteria (LAB). Lactobacillus, when given a favorable environment, will convert carbohydrates – sugars and starches – into lactic acid. The lactic acid environment then prevents other microorganisms from colonizing the food and prevents further decomposition. There are many different strains of lactobacillus.
Lactobacillus in conjunction with Saccharomyces cerevisiae, a yeast, will convert flour and water and give us sourdough bread. Yogurt is fermented with Streptococcus thermophilus and Lactobacillus
Why do we ferment food?
We do not have to use the process of fermentation to preserve food. We have dehydration, canning, refrigeration and freezing as good methods of keeping food safe. The main reason we practice fermentation today is to take advantage of the health benefits that are realized with eating fermented foods. Fermented foods add live cultures to our food - probiotics.
How do you ferment vegetables?
Fermentation is managed by creating a favorable environment for the lactobacillus to grow. In most vegetable ferments, this is done with non-iodized salt. Limiting the exposure to air also helps this process and keeps undesirable bacteria away from the food.
Main Ingredients
Water - use non-chlorinated water. To remove chlorine, boil water and let it cool. Or use filtered water. Bottled water is fine but not do not use distilled water.
Salt - non-iodized salt without any anti-caking ingredients. It is best to weigh the salt for accuracy. See below for more information.
Containers - a large food-safe container with a way to keep vegetables submerged and a lid that will allow gases to escape. More on containers from the National Center for Home Food Preservation.
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Publication from Colorado State:
Understanding and Making Kombucha
Canning
When canning home-preserved foods:
- Use scientifically-tested, up-to-date recipes such as those shown in this resource guide, Home Food Preservation Recipes and Information
- Follow directions carefully and do not change the measurements of fruit, vegetables, or acid.
- Adjust processing time for altitude.
- Date home-preserved foods and store them no more than 12 months between 50-70 degrees Fahrenheit. Avoid direct sunlight.
Safe Methods of Canning Vegetables